It seems that there are little to no difficulty increases past wave 30, when bombers are introduced. This is a problem because, unless it's all new players, most games reach this wave without incident, and beyond this, groups only ever lose because players quit out of boredom. I understand there is a hard mode (which may be another discussion entirely), but normal mode needs some changes in difficulty, at the very least after wave 30.

We discussed in-game some possibilities: more spearmen or a spearmen only round, more bombers (I believe this has already been tried and people didn't like it?), spawning "boss" mobs in multiple numbers instead of just one (i.e. skeleton king, wave commander), tanks with more or tougher mobs inside them.

My favorite idea, though, is giving some mobs the "donor" weapons once a certain round has been reached. Then, for every round afterwards, increase the probability that a mob spawns with this weapon or the "donor" weapon mob is spawned. Progressive difficulty is exactly what this game mode needs, and I think that's a fun way to satisfy that requirement. At the same time, it includes the new content that you've been working on.